U.S. patent application number 15/830400 was filed with the patent office on 2018-06-07 for image forming apparatus.
This patent application is currently assigned to Konica Minolta, Inc.. The applicant listed for this patent is Konica Minolta, Inc.. Invention is credited to Masayuki Fukunaga, Takaki Kato, Yuji Kobayashi.
Application Number | 20180157941 15/830400 |
Document ID | / |
Family ID | 62243220 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180157941 |
Kind Code |
A1 |
Kobayashi; Yuji ; et
al. |
June 7, 2018 |
IMAGE FORMING APPARATUS
Abstract
An image forming apparatus includes: a conveying path on which a
recording medium is conveyed; an image capturer that includes a
light source and radiates light from the light source to capture
the recording medium being conveyed at different timings to
generate at least two images including a first image and a second
image; and a movement amount calculator that calculates a movement
amount of the recording medium between capturing timings of the
first and second images, wherein the movement amount calculator:
calculates an index distance which is a distance in a conveying
direction of a pattern formed by reflected light from the recording
medium; calculates a ratio between the index distance and a
reference distance used for comparison with the index distance; and
calculates a movement amount of the recording medium between the
capturing timings of the first and second images.
Inventors: |
Kobayashi; Yuji;
(Toyohashi-shi, JP) ; Kato; Takaki; (Toyoake-shi,
JP) ; Fukunaga; Masayuki; (Toyohashi-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Konica Minolta, Inc. |
Tokyo |
|
JP |
|
|
Assignee: |
Konica Minolta, Inc.
Tokyo
JP
|
Family ID: |
62243220 |
Appl. No.: |
15/830400 |
Filed: |
December 4, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 1/00594 20130101;
G06K 15/1219 20130101; G06K 15/16 20130101; H04N 1/00602 20130101;
H04N 1/00652 20130101 |
International
Class: |
G06K 15/16 20060101
G06K015/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2016 |
JP |
2016-236774 |
Claims
1. An image forming apparatus comprising: a conveying path on which
a recording medium is conveyed; an image capturer that includes a
light source and radiates light from the light source to capture
the recording medium being conveyed at different timings to
generate at least two images including a first image and a second
image; and a movement amount calculator that calculates a movement
amount of the recording medium between capturing timings of the
first and second images, wherein the movement amount calculator:
calculates an index distance which is a distance in a conveying
direction of a pattern formed by reflected light from the recording
medium based on at least one image out of the first and second
images; calculates a ratio between the index distance and a
reference distance used for comparison with the index distance; and
calculates a movement amount of the recording medium between the
capturing timings of the first and second images based on the
ratio, the first image, and the second image.
2. The image forming apparatus according to claim 1, wherein the
light source includes a laser device.
3. The image forming apparatus according to claim 1, wherein the
movement amount calculator: calculates a first distance based on
the first image and the second image; and corrects the first
distance in accordance with the ratio to calculate the movement
amount.
4. The image forming apparatus according to claim 1, wherein the
movement amount calculator: corrects the first image and the second
image based on the ratio; and calculates the movement amount based
on the corrected first image and the corrected second image.
5. The image forming apparatus according to claim 1, wherein the
movement amount calculator calculates, as the index distance, an
average value of distances of the patterns in the conveying
direction in a plurality of images captured by the image
capturer.
6. The image forming apparatus according to claim 5, further
comprising a conveying roller arranged on a downstream side or an
upstream side of an irradiation position of the light source in the
conveying path, wherein the image capturer continuously captures
images over at least a rotation cycle of the conveying roller, and
the movement amount calculator calculates, as the index distance,
an average value of distances of the patterns in the conveying
direction in the plurality of continuously captured images.
7. The image forming apparatus according to claim 6, wherein the
movement amount calculator calculates, as the index distance, an
average value of distances of the patterns in the conveying
direction in a plurality of images continuously captured over a
period of an integral multiple of the rotation cycle of the
conveying roller among the plurality of continuously captured
images.
8. The image forming apparatus according to claim 1, further
comprising: a conveying roller arranged on a downstream side or an
upstream side of an irradiation position of the light source in the
conveying path; a sensor that senses a rotation angle of the
conveying roller; and a storage that stores a relationship between
the rotation angle of the conveying roller and a correction
coefficient, wherein the movement amount calculator corrects a
distance in the conveying direction of the pattern based on at
least one image out of the first and second images on the basis of
a correction coefficient corresponding to the rotation angle of the
conveying roller sensed by the sensor at a capturing timing of the
at least one image to calculate the index distance.
9. The image forming apparatus according to claim 1, wherein the
reference distance is a distance in the conveying direction of the
pattern in an image captured by the image capturer in a state where
the image capturer and the conveying direction are parallel.
10. The image forming apparatus according to claim 1, wherein the
image capturer further comprises an imaging lens having
telecentricity.
Description
[0001] The entire disclosure of Japanese patent Application No.
2016-236774, filed on Dec. 6, 2016, is incorporated herein by
reference in its entirety.
BACKGROUND
Technological Field
[0002] This disclosure relates to an image forming apparatus and,
more particularly, to a technique for sensing a conveying speed of
a recording medium in an image forming apparatus.
Description of the Related Art
[0003] Conventionally, a device for measuring the speed of a moving
object in a non-contact manner is used for various types of
products. For example, some image forming apparatuses, such as a
multi-functional peripheral (MFP), include an image pickup element
that picks up an image of a conveying path to specify the conveying
speed of a recording medium from the image picked up by the image
pickup element. For example, JP 2010-134190 A discloses a technique
for specifying the conveying speed of a recording medium by
processing each of two or more images picked up with respect to a
certain recording medium using Fourier transform.
[0004] Meanwhile, JP 2011-213463 A and JP 2011-207547 A disclose a
technique for specifying the conveying speed by capturing two
images of a recording medium being conveyed at different timings
and performing pattern matching on the two picked-up images.
[0005] For example, a movement amount detection device disclosed in
JP 2011-207547 A discloses a configuration including a first
illuminator 10 and a second illuminator 11, in which a set of
images having a relationship with a higher degree of similarity
among the similarity between first images captured by the first
illuminator 10 and the similarity between second images captured by
the second illuminator 11 is used to detect the movement amount of
a print medium P (refer to "Abstract").
[0006] However, the technique for obtaining the conveying speed of
the recording medium by pattern matching as in JP 2011-213463 A and
JP 2011-207547 A is easy to erroneously detect the moving
destination due to a lot of similar patterns on the surface of the
recording medium.
[0007] In addition, since the movement amount detection device
disclosed in JP 2011-207547 A requires a plurality of light sources
for calculating the movement amount, the production cost of the
movement amount detection device increases.
[0008] Although the technique disclosed in JP 2010-134190 A can
suppress erroneous detection of the moving destination of the
moving object as described above, an error in the calculated
conveying speed of the recording medium could increase, for
example, in a case where the recording medium is inclined with
respect to a conveying path. Therefore, there is a need for a
technique capable of more accurately obtaining the movement amount
of a moving object.
SUMMARY
[0009] The present disclosure has been made to solve the
above-described problems and an object of one aspect is to provide
an image forming apparatus capable of more accurately obtaining a
conveying speed of a recording medium being conveyed than in the
past.
[0010] To achieve the abovementioned object, according to an aspect
of the present invention, an image forming apparatus reflecting one
aspect of the present invention comprises: a conveying path on
which a recording medium is conveyed; an image capturer that
includes a light source and radiates light from the light source to
capture the recording medium being conveyed at different timings to
generate at least two images including a first image and a second
image; and a movement amount calculator that calculates a movement
amount of the recording medium between capturing timings of the
first and second images, wherein the movement amount calculator:
calculates an index distance which is a distance in a conveying
direction of a pattern formed by reflected light from the recording
medium based on at least one image out of the first and second
images; calculates a ratio between the index distance and a
reference distance used for comparison with the index distance; and
calculates a movement amount of the recording medium between the
capturing timings of the first and second images based on the
ratio, the first image, and the second image.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The objects, advantages, aspects, and features provided by
one or more embodiments of the invention will become more fully
understood from the detailed description given hereinbelow and the
appended drawings which are given by way of illustration only, and
thus are not intended as a definition of the limits of the present
invention:
[0012] FIGS. 1A and 1B are conceptual diagrams schematically
illustrating a method of calculating a conveying speed of a
recording medium according to an embodiment;
[0013] FIG. 2 is a diagram for explaining a configuration example
of an image forming apparatus;
[0014] FIG. 3 is a diagram for explaining a configuration example
of a sensor unit;
[0015] FIG. 4 is a diagram for explaining a control structure of a
calculator according to a first embodiment;
[0016] FIG. 5 is a flowchart for explaining control for calculating
a conveying speed of a sheet being conveyed;
[0017] FIG. 6 is a diagram for explaining a control structure of a
calculator according to a second embodiment;
[0018] FIG. 7 is a flowchart for explaining control for calculating
the conveying speed of the sheet being conveyed, according to the
second embodiment;
[0019] FIG. 8 is a diagram for explaining eccentricity in a fixing
roller;
[0020] FIG. 9 is a diagram for explaining a relationship between
eccentricity of a fixing roller and a ratio of an index distance to
a reference distance;
[0021] FIG. 10 is a diagram for explaining a control structure of a
calculator according to a third embodiment;
[0022] FIG. 11 is a flowchart for explaining control for
calculating the conveying speed of the sheet being conveyed,
according to the third embodiment;
[0023] FIG. 12 is a flowchart for explaining control for
calculating the conveying speed of the sheet being conveyed,
according to a fourth embodiment;
[0024] FIG. 13 is a diagram for explaining a configuration example
of an image forming apparatus according to a fifth embodiment;
[0025] FIG. 14 is a diagram for explaining a control structure of a
calculator according to the fifth embodiment;
[0026] FIG. 15 is a flowchart for explaining control for
calculating the conveying speed of the sheet being conveyed,
according to the fifth embodiment; and
[0027] FIG. 16 is a diagram illustrating how a distance between the
sheet and a lens varies.
DETAILED DESCRIPTION OF EMBODIMENTS
[0028] Hereinafter, one or more embodiments of the present
invention will be described in detail with reference to the
drawings. However, the scope of the invention is not limited to the
disclosed embodiments. In the following description, the same
members are denoted by the same reference numerals. The names and
functions thereof are also the same. Therefore, detailed
description thereof will not be repeated. Note that the respective
embodiments and configurations described below may be selectively
combined as appropriate.
[0029] (Technical Thought)
[0030] FIGS. 1A and 1B are conceptual diagrams schematically
illustrating a method of calculating a conveying speed of a
recording medium according to an embodiment. Referring to FIG. 1A,
an image forming apparatus 100 according to an embodiment has a
conveying path R1, an image capturer 70, and a field-programmable
gate array (FPGA) 86. A sheet S as a recording medium is being
conveyed on the conveying path R1.
[0031] The image capturer 70 captures an image of the sheet S being
conveyed at different timings to generate at least two images
including a first image and a second image and outputs the
generated images to the FPGA 86.
[0032] A calculator 90 of the FPGA 86 calculates a movement amount
of the sheet S between the capturing timings of the first and
second images based on these two images.
[0033] However, when the positional relationship between the image
capturer 70 and the sheet S varies, it could become difficult to
precisely calculate the movement amount of this sheet S.
[0034] It is assumed that, at the time of manufacturing the image
forming apparatus 100, the image capturer 70 is attached at a
position of a state 70A represented by a solid line. It is assumed
that the image capturer 70 and the conveying path R1 are parallel
in this state.
[0035] The image capturer 70 irradiates the sheet S with laser
light from a laser light source 81 to be described later and
detects reflected light from the sheet S. In one aspect, it is
assumed that an aperture (not illustrated) of the laser light
source 81 has an elliptical shape extending in a conveying
direction. In this case, the image capturer 70 in the state 70A
detects a speckle pattern 110A indicated by a solid line in FIG.
1B. The length of this speckle pattern 110A in the conveying
direction, that is, the major axis is a length L1.
[0036] It is assumed that, by use of the image forming apparatus
100, the image capturer 70 has moved to a position of a state 70B
represented by a broken line. As a result, the image capturer 70 in
the state 70B and the conveying path R1 are no longer parallel.
[0037] The image capturer 70 in the state 70B detects a speckle
pattern 110E indicated by a broken line in FIG. 1B. The major axis
of this speckle pattern 110B is a length L2.
[0038] As illustrated in FIG. 1B, the length L2 of the speckle
pattern 110B in the conveying direction is shorter than the length
L1 of the speckle pattern 110A in the conveying direction. This is
because the image capturer 70 (a sensor surface of a
two-dimensional sensor included therein) in the state 70B and the
conveying direction of the sheet S are not parallel and thus, the
speckle pattern captured by the image capturer 70 in the state 70B
is reduced in size in the conveying direction than the actual
speckle pattern.
[0039] Accordingly, when the movement amount of the sheet S is
calculated based on the first image and the second image captured
by the image capturer 70 in the state 70B, the FPGA 86 calculates a
movement amount smaller than the actual movement amount.
[0040] Note that the aspect in which the image capturer 70 and the
sheet S are not parallel is not limited to the aspect in which the
image capturer 70 is inclined as in the state 70B. In another
aspect, the sheet S can be inclined with respect to the conveying
path R1. Also in such an aspect, the image capture'. 70 and the
sheet S are not parallel and the speckle pattern captured by the
image capturer 70 can be reduced in size in the conveying direction
than the actual speckle pattern.
[0041] The image forming apparatus 100 according to an embodiment
can solve such disadvantages. The image forming apparatus 100
according to the embodiment measures the length L1 in the conveying
direction of the speckle pattern 110A captured by the image
capturer 70 in the state 70A and stores the measured length L1 to a
storage 92 as a reference distance .PHI.s.
[0042] The calculator 90 according to the embodiment measures an
index distance .PHI.1, which is a distance (L2) in the conveying
direction in the speckle pattern 110B, based on at least one image
out of the first image and the second image captured by the image
capturer 70 in the state 70B.
[0043] The calculator 90 calculates a ratio of the reference
distance .PHI.s to the index distance .PHI.1. The calculator 90
calculates a temporary movement amount of the sheet S based on the
first image and the second image captured by the image capturer 70
in the state 70B. The calculator 90 corrects this temporary
movement amount using the above ratio and settles the movement
amount of the sheet S.
[0044] According to the above configuration, the image forming
apparatus 100 according to the embodiment can precisely calculate
the movement amount of the sheet S even when the positional
relationship between the image capturer 70 (the sensor surface of
the two-dimensional sensor included therein) and the sheet S is
altered. A specific configuration and control of the image forming
apparatus 100 that can realize such control will be described
below.
First Embodiment
(Configuration of Image Forming Apparatus 100)
[0045] FIG. 2 is a diagram for explaining a configuration example
of the image forming apparatus 100. FIG. 2 illustrates the image
forming apparatus 100 as a color printer. The image forming
apparatus 100 as a color printer will be described hereinafter, but
the image forming apparatus 100 is not limited to a color printer.
For example, the image forming apparatus 100 may be a monochrome
printer, or may be a multi-functional peripheral (MFP) including a
monochrome printer, a color printer, and a FAX.
[0046] As illustrated in FIG. 2, the image forming apparatus 100
includes an image former 1, an intermediate transferer 2, a sheet
supplier 3, a fixing device 4, a sheet winder 5, a controller 6,
and the like. The image forming apparatus 100 is connected to a
network (for example, a local area network (LAN)) and, when
accepting an instruction to execute a printing job from an external
terminal device (not illustrated), forms a color image of yellow
(Y), magenta (M), cyan (C), and black (K) colors based on the
instruction.
[0047] The image former 1 includes imaging units 10Y to 10K
corresponding to Y to K colors, respectively. The imaging unit 10Y
charges a surface of a photosensitive drum 11Y rotating at a
constant speed. When an electrostatic latent image is formed on the
charged photosensitive drum 11Y by exposure scanning on an exposed
area, this electrostatic latent image is developed with toner of Y
color and a developed Y color toner image is primarily transferred
onto an intermediate transfer belt 21 in an electrostatic
manner.
[0048] The other imaging units 10M, 10C, and 10K also execute the
respective processes of charging, exposure, development, and
primary transfer similar to those of the imaging unit 10Y and
primarily transfer an M color toner image on a photosensitive drum
11M, a C color toner image on a photosensitive drum 11C, and a K
color toner image on a photosensitive drum 11K, respectively, onto
the intermediate transfer belt 21. In FIG. 2, formation timings of
the toner images of Y to K colors are set such that the toner
images of Y to K colors representing an original image of one page
are multiply transferred on the intermediate transfer belt 21.
These formation timings are set in accordance with the surface
speed of the intermediate transfer belt 21. The surface speed of
the intermediate transfer belt 21 is defined by the rotation speed
of a driving roller 22 that stretches the intermediate transfer
belt 21. Accordingly, it is required to grasp the precise rotation
speed of the driving roller 22 (in other words, the conveying speed
of the sheet S at a downstream area of the driving roller 22). The
reason is that, when the rotation speed of the driving roller 22 is
erroneously sensed, the timings of superimposing the toner images
of Y to K colors are out of sync and color misregistration occurs
in the sheet S (recording medium).
[0049] The intermediate transferer 2 includes the intermediate
transfer belt 21, the driving roller 22 and driven rollers 23, 24,
and 25 that stretch the intermediate transfer belt 21, a secondary
transfer roller 26, and the like.
[0050] The driving roller 22 is rotated by a rotational driving
force of a belt motor 71 and causes the intermediate transfer belt
21 to circulate in a direction indicated by arrows in FIG. 2. The
belt motor 71 is constituted by, for example, a direct current (DC)
brushless motor. The driven rollers 23, 24, and 25 are driven to
rotate as the intermediate transfer belt 21 circulates.
[0051] During the circulation of the intermediate transfer belt 21,
the toner images of Y to K colors formed by the imaging units 10Y
to 10K are multiply transferred onto a circumferential surface of
the intermediate transfer belt 21.
[0052] The toner images of Y to K colors multiply transferred onto
the intermediate transfer belt 21 are conveyed by the circulation
of the intermediate transfer belt 21 toward the secondary transfer
roller 26 arranged so as to oppose the driving roller 22 with the
intermediate transfer belt 21 interposed therebetween.
[0053] The secondary transfer roller 26 is in contact with the
circumferential surface of the intermediate transfer belt 21 at a
secondary transfer position 261 of the intermediate transfer belt
21 and is driven to rotate as the intermediate transfer belt 21
circulates.
[0054] The sheet supplier 3 sends the elongated sheet S from a roll
sheet 33 wound around a rotation shaft 31 to a paper feed adjuster
34 via a supply roller 32. The paper feed adjuster 34 conveys the
sheet S from the supply roller 32 toward a conveying roller 35 of a
main body 9 of the image forming apparatus 100. The paper feed
adjuster 34 holds the elongated sheet S in a slackened state so as
to absorb a difference in speed between the conveying speed of the
sheet S sent out from the roll sheet 33 in the sheet supplier 3 and
the conveying speed of the sheet S in the main body 9, thereby
adjusting the feeding of the sheet S to the main body 9. In
addition, not only plain paper but also label paper, for example,
may be used as the sheet S in some cases.
[0055] The sheet S supplied to the conveying roller 35 is wound up
by a winding roller 51 via the secondary transfer position 261, the
fixing device 4, a discharge roller 46, a paper discharge adjuster
53 of the sheet winder 5, and a conveying roller 52. The paper
discharge adjuster 53 holds the elongated sheet S in a slackened
state so as to absorb a difference in speed between the conveying
speed of the sheet S in the main body 9 and the conveying speed of
the sheet S by the winding roller 51 of the sheet winder 5, thereby
adjusting the discharge of the sheet S from the main body 9.
[0056] During the winding of the sheet S, the toner images of Y to
K colors multiply transferred onto the intermediate transfer belt
21 are secondarily transferred by the secondary transfer roller 26
in an electrostatic manner collectively on a front side surface of
the sheet S passing through the secondary transfer position 261
(that is, a side in contact with the intermediate transfer belt
21). In a case where a plurality of pages of toner images are
formed on the intermediate transfer belt 21 at a constant interval
in a belt circulation direction, the toner images of respective
pages are secondarily transferred onto the sheet S one by one in
order while the elongated sheet S passes through the secondary
transfer position 261. The toner image of each page secondarily
transferred onto the sheet S is conveyed to the fixing device 4
together with the sheet S being wound.
[0057] The fixing device 4 includes a heating roller 40 in a
cylindrical shape having a heater 43 inserted therein, a fixing
roller 41 in a cylindrical shape, and a pressure roller 42 brought
into pressure contact with the fixing roller 41 with a
predetermined pressure at a nip area 45 with the fixing roller 41.
The fixing device 4 makes the heating roller 40 hot by heating the
heater 43 to a predetermined temperature. As the heating roller 40
rotates, heat is transferred to the nip area 45 between the fixing
roller 41 and the pressure roller 42. The fixing device 4 maintains
the temperature of the nip area 45 at a temperature necessary for
fixing the toner (for example, 150.degree. C.).
[0058] The fixing roller 41 is driven in a direction of an arrow in
FIG. 2 by a fixing motor 72 constituted by a DC brushless motor and
rotates about a rotation shaft 47. Note that the heating roller 40
may drivingly rotate instead of the fixing roller 41. The pressure
roller 42 is driven to rotate by the fixing roller 41. The fixing
roller 41 and the pressure roller 42 pinch the sheet S to convey
and at the same time thermally fix the toner image on the front
side of the sheet S by heating and pressurizing while this toner
image after the secondary transfer onto the sheet S passes through
the nip area 45.
[0059] The sheet S being wound is conveyed across the fixing roller
41 and the secondary transfer roller 26. When a sheet area Sd of
the sheet S located between the fixing roller 41 and the secondary
transfer roller 26 slackens during this conveyance, wrinkles
sometimes occur in the sheet S at the nip area 45.
[0060] Therefore, in order to prevent the occurrence of wrinkles on
the sheet S, a certain degree of tension acts on the sheet area Sd
in a sheet conveying direction. This tension is generated, for
example, by driving the rotation speed of the fixing roller 41
faster by a constant value than the rotation speed of the secondary
transfer roller 26.
[0061] The conveying speed of the sheet S is sensed by a sensor
unit 44. The sensor unit 44 is disposed at a position in the
vicinity of the nip area 45 on an upstream side of the nip area 45
in the sheet conveying direction and on a lower side of a position
P in the conveying path R1 of the sheet S. The sensor unit 44
measures the conveying speed of a back side surface of the sheet S
pinched and conveyed by the fixing roller 41 and the pressure
roller 42 (that is, a side on which the toner image is not
transferred). The sensor unit 44 measures the conveying speed of
the sheet surface at a constant interval (for example, every 1 ms)
during the conveyance of the sheet S and sends a result of the
measurement to the controller 6.
[0062] Note that, in the example illustrated in FIG. 2, the sensor
unit 44 is arranged between the secondary transfer roller 26 and
the fixing device 4, but the arrangement position of the sensor
unit 44 is not limited thereto. For example, the sensor unit 44 may
be arranged between the conveying roller 35 and the secondary
transfer roller 26, or may be arranged on an upstream side of the
conveying roller 35. In addition, a configuration including a
plurality of sensor units 44 arranged in the image forming
apparatus 100 may be employed.
[0063] (Configuration of Sensor Unit 44)
[0064] FIG. 3 is a diagram for explaining a configuration example
of the sensor unit 44. In the example illustrated in FIG. 3, the
sheet S is being conveyed to the fixing device 4.
[0065] The sensor unit 44 includes the image capturer 70, an
analog-to-digital converter (ADC) 85, the FPGA 86, and a ROM 92.
The sensor unit 44 functions as a movement amount sensing device
for calculating the movement amount of the sheet S being conveyed
during a certain period using the speckle pattern formed by the
reflected light from the sheet S on a two-dimensional sensor 84. In
other words, the sensor unit 44 is a non-contact type sensor that
measures the conveying speed of the sheet S.
[0066] The image capturer 70 includes the laser light source 81, a
lens 82 which is a collimator lens, a lens 83, and the
two-dimensional sensor 84.
[0067] The laser light source 81 includes an aperture (diaphragm)
(not illustrated). In an embodiment, this aperture may be
elliptical. Note that, in another embodiment, the shape of the
aperture is not limited to an elliptical shape and may have a
quadrangular shape or another shape.
[0068] The two-dimensional sensor 84 has a plurality of
photoelectric conversion elements arrayed in the conveying
direction of the sheet S (hereinafter also referred to as "lateral
direction") and an orthogonal direction orthogonal to this
conveying direction (hereinafter also referred to as "longitudinal
direction"). In an embodiment, the number of photoelectric
conversion elements arrayed in the lateral direction is greater
than the number of photoelectric conversion elements arrayed in the
longitudinal direction, whereby the calculator 90 can calculate the
movement amount of the sheet S more accurately.
[0069] In the manufacturing stage of the image forming apparatus
100, the laser light source 81 is set so as to emit laser light
toward a predetermined irradiation position Sp on the conveying
path R1. The laser light emitted from the laser light source 81
travels through the lens 82 and a surface Sa of the sheet S being
conveyed is irradiated therewith.
[0070] An angle .theta.2 formed between the laser light incident on
the surface Sa of the sheet S and the surface Sa of the sheet S is
45.degree. in FIG. 3. Note that the angle .theta.2 is not limited
to 45.degree. and may be any angle within the range of 20.degree.
to 45.degree., for example.
[0071] The surface Sa of the sheet S can be said to be a roughened
surface having minute irregularities from a microscopic viewpoint
and, when this roughened surface is irradiated with laser light
(coherent light), a granular pattern called speckle is generated.
The speckle is generated because beams of light with different
phases overlap due to superimposition of beams of scattered light
caused by irregular reflection of laser light from respective
places on the roughened surface.
[0072] Reflected light reflected from the surface Sa of the sheet S
at an angle .theta.1 (for example, 90.degree.) among the laser
light having generated the speckle travels through the lens 83
provided just below the irradiation position Sp and is focused on a
sensing surface of the two-dimensional sensor 84 as a light
receiver. As a result, a speckle pattern generated on the surface
Sa of the sheet S positioned immediately above the sensing surface
of the two-dimensional sensor 84 can be sensed thereon.
[0073] The speckle does not change unless the sheet S moves but
changes as the sheet S moves. As the sheet S is conveyed, an
irregular area on the roughened surface passing through the
irradiation position Sp of laser light changes at each time point
and the state of superimposition of the irregularly reflected light
of the laser also changes at each time point.
[0074] The rate of change of the speckle depends on the conveying
speed of the sheet S and the amount of received laser light on the
sensing surface of the two-dimensional sensor 84 also changes due
to a change in speckle. Therefore, by sensing a temporal change in
the amount of received laser light on the sensing surface of the
two-dimensional sensor 84, it is possible to measure the conveying
speed of the surface of the sheet S. Thus, the irradiation position
Sp of the laser light on the sheet S can be regarded as a
measurement position of the conveying speed of the sheet
surface.
[0075] The two-dimensional sensor 84 outputs an analog voltage
signal according to the amount of received laser light focused on
the sensing surface thereof to the analog-to-digital converter
(ADC) 85 at a constant cycle, for example, every several
milliseconds.
[0076] The ADC 85 converts the analog voltage signal from the
two-dimensional sensor 84 into a digital signal each time the
digital signal is received at a constant cycle and outputs the
converted digital signal to the FPGA 86.
[0077] The FPGA 86 includes the calculator 90. Based on the two
images captured at different timings, the index distance .PHI.1,
and the reference distance .PHI.s used for the comparison with the
index distance .PHI.1, the calculator 90 calculates the movement
amount of the sheet S between the capturing timings of the two
images. The index distance .PHI.1 may be the length in the
conveying direction (major axis) of the speckle pattern in at least
one image out of the above-described two images. The reference
distance .PHI.s is assumed to be the length in the conveying
direction (major axis) of the speckle pattern captured in a state
where the sheet S and the image capturer 70 (the sensor surface of
the two-dimensional sensor 84 included therein) are in a parallel
relationship. In one aspect, the reference distance .PHI.s may be
the length in the conveying direction of the speckle pattern
captured at the time of manufacturing the image forming apparatus
100. The reference distance .PHI.s is saved in the ROM 92. The
specific control of the calculator 90 will be described later with
reference to FIGS. 4 and 5.
[0078] The calculator 90 calculates the conveying speed of the
sheet S based on an interval between the capturing timings of the
two images and the calculated movement amount. The calculator 90
outputs the calculated conveying speed of the sheet S to the
controller 6. The controller 6 can be constituted by, for example,
a central processing unit (CPU).
[0079] The controller 6 acquires the conveying speed of the sheet S
being conveyed from the sensor unit 44. The controller 6 controls
the rotation speed of the fixing motor 72 driving the fixing roller
41 based on the conveying speed of the sheet S and assigns the
conveying speed of the sheet S as a target speed defined in
advance. As a result, the controller 6 can suppress the occurrence
of wrinkles on the sheet S at the nip area 45, for example.
[0080] Furthermore, the controller 6 may additionally control the
rotation speed of a secondary transfer motor 73 driving the driving
roller 22 based on the conveying speed of the sheet S acquired from
the sensor unit 44. At this time, the controller 6 controls the
secondary transfer motor 73 such that the rotation speed of the
fixing motor 72 is faster than the rotation speed of the secondary
transfer motor 73. As a result, the sheet S is pulled by the fixing
device 4 and wrinkles can be prevented from occurring on the sheet
S at the nip area 45.
[0081] Furthermore, based on the conveying speed of the sheet S
acquired from the sensor unit 44, the controller 6 may control
timings at which the toner images formed on the photosensitive
drums 11M, 11C, and 11K are primarily transferred onto the
intermediate transfer belt. As a result, the image forming
apparatus 100 can suppress occurrence of color misregistration in
the document. In particular, when a long sheet S (roll sheet 33) as
illustrated in FIG. 2 is used as a recording medium, since the
recording medium is conveyed while being pulled by the fixing
device 4 (the nip area 45 located therein), the conveying speed of
the recording medium at the secondary transfer position 261 (that
is, the surface speed of the intermediate transfer belt 21) can be
affected by these members of the fixing device 4. Regarding this
respect, the image forming apparatus 100 according to the
embodiment regulates a primary transfer timing of each color based
on the precise conveying speed of the sheet S (the surface speed of
the intermediate transfer belt 21) from the sensor unit 44, thereby
being able to suppress color misregistration and to make the image
formed on the sheet S (recording medium) more beautiful.
[0082] (Control Structure of Calculator 90)
[0083] FIG. 4 is a diagram for explaining a control structure of
the calculator 90 according to the first embodiment. The calculator
90 includes a discrete Fourier transform unit 410, a normalization
processing unit 420, a synthesis unit 430, an inverse discrete
Fourier transform unit 440, an index distance calculation unit 450,
and a distance correction unit 460.
[0084] The discrete Fourier transform unit 410 executes discrete
Fourier transform processing on the first image and the second
image captured by the image capturer 70 at different timings to
decompose data thereof into each wavenumber component. The discrete
Fourier transform unit 410 outputs the data decomposed into each
wavenumber component to the normalization processing unit 420.
[0085] The normalization processing unit 420 multiplies the
amplitude corresponding to the first image by the amplitude
corresponding to the second image for each wavenumber component. As
a result, the normalization processing unit 420 normalizes the
magnitude of amplitude of each wavenumber and extracts phase
information on each wavenumber. The normalization processing unit
420 outputs the extracted phase information to the synthesis unit
430.
[0086] The synthesis unit 430 synthesizes the phase information
extracted for each wavenumber. The synthesis unit 430 calculates a
shift amount of a peak based on the synthesized phase information
to derive a phase difference between the first image and the second
image. The synthesis unit 430 outputs the derived phase difference
to the inverse discrete Fourier transform unit 440.
[0087] The inverse discrete Fourier transform unit 440 performs
inverse discrete Fourier transform processing on the derived phase
difference in a wavenumber space, thereby transforming this phase
difference into a temporary movement amount which is a distance in
the real space. The inverse discrete Fourier transform unit 440
outputs the transformed temporary movement amount to the distance
correction unit 460.
[0088] The index distance calculation unit 450 acquires a length d1
of the speckle pattern in the conveying direction in the first
image and a length d2 of the speckle pattern in the conveying
direction in the second image by image processing.
[0089] As an example, the index distance calculation unit 450 scans
a luminance distribution in the first image in the lateral
direction or the longitudinal direction and specifies a position
where a vertical relationship with a threshold luminance is
reversed as an edge (end) of the speckle pattern. The index
distance calculation unit 450 may specify an area where the
distance (number of pixels) between edges is longest in the
conveying direction and specify this distance as the length d1 of
the speckle pattern in the conveying direction.
[0090] The index distance calculation unit 450 may specify an
average value of the acquired length d1 and length d2 as the index
distance .PHI.1. The index distance calculation unit 450 outputs
the specified index distance .PHI.1 to the distance correction unit
460.
[0091] The distance correction unit 460 accesses the ROM 92 to
acquire the reference distance .PHI.s. The distance correction unit
460 calculates the ratio of the reference distance .PHI.s to the
index distance .PHI.1. The distance correction unit 460 multiplies
the temporary movement amount input from the inverse discrete
Fourier transform unit 440 by the calculated ratio to calculate the
movement amount of the sheet S between the capturing timings of the
first image and the second image.
[0092] Note that, in an embodiment, the distance correction unit
460 may treat this ratio as one when the ratio of the reference
distance .PHI.s to the index distance .PHI.1 is less than one.
[0093] (Flow of Control for Calculating Conveying Speed--Part
1)
[0094] FIG. 5 is a flowchart for explaining control for calculating
the conveying speed of the sheet S being conveyed. The processing
illustrated in FIG. 5 can be realized by the FPGA 86. In another
aspect, part or all of the processing may be realized by the
controller 6 (CPU) or may be realized by other hardware. Note that
the series of items of processing illustrated in FIG. 5 can be
executed in response to the input of a print job to the image
forming apparatus 100. In addition, it is assumed that these
conditions are the same in flowcharts illustrated in FIGS. 7, 11,
and 14.
[0095] In step S505, the FPGA 86 calculates the interval of
capturing the image (speckle pattern) by the image capturer 70 in
accordance with a set speed. The set speed is the conveying speed
of the sheet S supposed by the voltage applied to the fixing motor
72 and the secondary transfer motor 73, or the like.
[0096] In step S510, the FPGA 86 sets a light amount catching time
(that is, a capturing interval) of the two-dimensional sensor 84
based on the calculated capturing interval. In one aspect, the FPGA
86 may set the capturing interval of the image capturer 70 to 1
ms.
[0097] In step S515, the FPGA 86 regulates the amount of the laser
light from the laser light source 81. For example, the FPGA 86 can
realize the above processing by adjusting the output of a PIN
photodiode included in the laser light source 81.
[0098] In step S520, the FPGA 86 starts a printing operation and
starts conveying the sheet S.
[0099] In step S525, the FPGA 86 initializes a variable N (for
example, sets to one). This variable N may be saved in, for
example, a random access memory (RAM) (not illustrated).
[0100] In step S530, the FPGA 86 captures an image of the sheet S
being conveyed using the image capturer 70 to generate an Nth
image.
[0101] In step S535, the FPGA 86 as the index distance calculation
unit 450 calculates a distance in the conveying direction of a
speckle pattern included in the Nth image, that is, an index
distance .PHI.N. The FPGA 86 may store the calculated index
distance .PHI.N to a storage such as a RAM (not illustrated).
[0102] In step S540, the FPGA 86 again captures an image of the
sheet S being conveyed using the image capturer 70 to generate an
(N+1)th image after the capturing interval set in step S510
elapses.
[0103] In step S545, the FPGA 86 calculates an index distance
.PHI.N+1 of a speckle pattern included in the (N+1)th image.
[0104] In step S550, based on the Nth image and the (N+1)th image,
the FPGA 86 as the calculator 90 calculates the temporary movement
amount of the sheet S between the capturing timings of these
images.
[0105] In step S555, the FPGA 86 calculates the average value of
the index distances .PHI.N and .PHI.N+1. Furthermore, the FPGA 86
calculates a ratio of the reference distance .PHI.s to the
calculated average value. Furthermore, the FPGA 86 multiplies the
temporary movement amount calculated in step S550 by the above
ratio to calculate the movement amount of the sheet S.
[0106] In step S560, the FPGA 86 calculates the conveying speed of
the sheet S from the capturing interval set in step S510 and the
movement amount of the sheet S. The FPGA 86 outputs the calculated
conveying speed to the controller 6.
[0107] In step S565, the FPGA 86 determines whether the print job
has ended. For example, when the print job is ended, the controller
6 notifies the FPGA 86 of that effect. As a result, the FPGA 86 can
make this determination.
[0108] When the FPGA 86 determines that the print job has ended
(YES in step S565), the FPGA 86 ends the series of items of
processing. When the FPGA 86 determines that the print job has not
ended yet (NO in step S565), the FPGA 86 returns the processing to
step S570.
[0109] In step S570, the FPGA 86 increments the variable N and then
returns the processing to step S540.
[0110] According to the above configuration, the image forming
apparatus 100 according to the embodiment can precisely calculate
the movement amount (conveying speed) of the sheet S even when the
positional relationship between the image capturer 70 (the sensor
surface of the two-dimensional sensor 84 included therein) and the
sheet S is altered because, for example, the image capturer 70 or
the sensor unit 44 including the image capturer 70 is inclined or
the sheet S is inclined with respect to the conveying path R1.
[0111] Furthermore, the controller 6 of the image forming apparatus
100 can control the rotation speed of the fixing motor 72, the
rotation speed of the secondary transfer motor 73, and the like
based on the precise conveying speed of the sheet S calculated by
the sensor unit 44. As a result, for example, the controller 6 can
suppress color misregistration in the sheet S (recording medium)
and prevent wrinkles from occurring on the sheet S at the nip area
45 of the fixing device 4.
Second Embodiment
[0112] The calculator 90 according to the first embodiment
calculates the temporary movement amount of the sheet S based on
the first image and the second image and then corrects the
temporary movement amount using the ratio of the reference distance
.PHI.s to the index distance .PHI.1, thereby calculating the
movement amount of the sheet S.
[0113] A calculator according to a second embodiment corrects the
luminance of the first image and the second image using the above
ratio and then calculates the movement amount of the sheet S based
on the corrected images. Hereinafter, the configuration of this
calculator and control for calculating the conveying speed of the
sheet S will be described. Note that an image forming apparatus
according to the second embodiment has the same structure as the
above-described structure of the image forming apparatus 100 except
that the image forming apparatus according to the second embodiment
has a calculator 90A to be described later instead of the
calculator 90. Accordingly, the detailed configuration of the image
forming apparatus according to the second embodiment will not be
repeatedly described.
[0114] (Control Structure of Calculator 90A)
[0115] FIG. 6 is a diagram for explaining a control structure of
the calculator 90A according to the second embodiment. Note that
members denoted by the same reference numerals as those in FIG. 4
are the same and therefore the description thereof will not be
repeated.
[0116] The calculator 90A differs from the calculator 90 described
with reference to FIG. 4 in that the calculator 90A has an
intensity correction unit 600 and does not have the distance
correction unit 460.
[0117] The intensity correction unit 600 accepts inputs of the
first image and the second image captured by an image capturer 70
at different timings. In addition, the intensity correction unit
600 accepts inputs of the index distances .PHI.1 and .PHI.2
calculated by an index distance calculation unit 450. This index
distance .PHI.1 represents the length of the speckle pattern in the
conveying direction in the first image and the index distance
.PHI.2 represents the length of the speckle pattern in the
conveying direction in the second image.
[0118] The intensity correction unit 600 calculates an average
value of the index distances .PHI.1 and .PHI.2. The intensity
correction unit 600 calculates a ratio of the reference distance
.PHI.s to this average value. The intensity correction unit 600
multiplies the luminance of each pixel in the first image and the
second image by this ratio to correct these images. The intensity
correction unit 600 outputs the corrected first image and second
image to a discrete Fourier transform unit 410.
[0119] In another aspect, the intensity correction unit 600 may
correct the luminance of each pixel of the first image using the
ratio of the reference distance .PHI.s to the index distance .PHI.1
and correct the luminance of each pixel of the second image using
the ratio of the reference distance .PHI.s to the index distance
.PHI.2.
[0120] (Flow of Control for Calculating Conveying Speed--Part
2)
[0121] FIG. 7 is a flowchart for explaining control for calculating
the conveying speed of the sheet S being conveyed, according to the
second embodiment. Note that processing denoted by the same
reference numerals as those in FIG. 5 is the same processing and
therefore the description thereof will not be repeated.
[0122] In step S710, the FPGA 86 calculates the ratio of the
reference distance .PHI.s to the index distance .PHI.N.
Furthermore, the FPGA 86 multiplies the luminance of each pixel in
the generated Nth image by the calculated ratio to correct the Nth
image.
[0123] Likewise in step S720, the FPGA 86 calculates the ratio of
the reference distance .PHI.s to the index distance .PHI.N+1.
Furthermore, the FPGA 86 multiplies the luminance of each pixel in
the generated (N+1)th image by the above ratio to correct the
(N+1)th image.
[0124] In step S730, based on the corrected Nth image and the
corrected (N+1)th image, the FPGA 86 as the calculator 90A
calculates the movement amount of the sheet S between the capturing
timings of these images.
[0125] By the configuration for previously correcting the luminance
of the generated image, as in the image forming apparatus 100
according to the first embodiment, the image forming apparatus
according to the second embodiment can precisely calculate the
movement amount of the sheet S even when the positional
relationship between the image capturer 70 (the sensor surface of a
two-dimensional sensor 84 included therein) and the sheet S is
altered.
Third Embodiment
[0126] As described above, when the sheet S is inclined with
respect to the conveying path R1, the positional relationship
between the image capturer 70 and the sheet S is altered and an
error in the movement amount of the sheet S could increase. One of
the causes of the inclination of the sheet S with respect to the
conveying path R1 is the eccentricity of the conveying roller
including the fixing roller 41 and the like. Therefore, an image
forming apparatus according to the third embodiment calculates the
movement amount of the sheet S in consideration of the eccentricity
of the conveying roller that conveys the sheet S. Hereinafter,
calculation control for the movement amount of the sheet S in this
image forming apparatus 100 according to the third embodiment will
be described.
[0127] Note that the image forming apparatus according to the third
embodiment has the same structure as the above-described structure
of the image forming apparatus 100 except that the image forming
apparatus according to the third embodiment has a calculator 90B to
be described later instead of the calculator 90. Accordingly, the
detailed configuration of the image forming apparatus according to
the third embodiment will not be repeatedly described.
[0128] (Eccentricity of Roller)
[0129] FIG. 8 is a diagram for explaining eccentricity in a fixing
roller 41. As illustrated in FIG. 8, a rotation shaft 47 of the
fixing roller 41 constituting a fixing device 4 deviates from the
center of the fixing roller 41 in some cases. When the fixing
roller 41 is eccentric in this manner, the inclination of the sheet
S with respect to a conveying path R1 periodically changes.
[0130] (Variation of Index Distance Due to Eccentricity)
[0131] FIG. 9 is a diagram for explaining a relationship between
eccentricity of the fixing roller 41 and the ratio of the index
distance .PHI.N to the reference distance .PHI.s. The lateral axis
in FIG. 9 represents the rotation angle of the fixing roller 41.
The longitudinal axis in FIG. 9 represents the ratio of the index
distance .PHI.N to the reference distance .PHI.s. The index
distance .PHI.N indicates a distance in the conveying direction of
a speckle pattern included in an image captured by an image
capturer 70 during one rotation of the fixing roller 41. In the
example in FIG. 9, it is assumed that the image capturer 70
generates 200 images following a predetermined capturing interval
while the fixing roller 41 makes one rotation. As a result, the
index distances .PHI.1-.PHI.200 are calculated. For example, the
index distance .PHI.50 represents a distance in the conveying
direction of a speckle pattern included in an image captured by the
image capturer 70 when the rotation angle of the fixing roller 41
is 90.degree..
[0132] A distribution 910 indicates the ratio between the index
distance 4N and the reference distance .PHI.s based on the images
captured by the image capturer 70 in a state in which the image
capturer 70 is not inclined from the time of manufacturing the
image forming apparatus (in a state in which the image capturer 70
and the conveying path R1 are parallel) and also the fixing roller
41 is not eccentric. In the distribution 910, it can be seen that
the ratio of the index distance .PHI.N to the reference distance
.PHI.s is one regardless of the rotation angle of the fixing roller
41.
[0133] A distribution 920 indicates the ratio between the index
distance .PHI.N and the reference distance .PHI.s based on the
images captured by the image capturer 70 in a state in which the
image capturer 70 is inclined from the time of manufacturing the
image forming apparatus and also the fixing roller 41 is not
eccentric. In the distribution 920, it can be seen that the ratio
of the index distance .PHI.N to the reference distance .PHI.s is
constant (0.995) regardless of the rotation angle of the fixing
roller 41.
[0134] A distribution 930 indicates the ratio between the index
distance .PHI.N and the reference distance .PHI.s based on the
images captured by the image capturer 70 in a state in which the
image capturer 70 is inclined from the time of manufacturing the
image forming apparatus and also the fixing roller 41 is eccentric.
In the distribution 930, it can be seen that the ratio of the index
distance .PHI.N to the reference distance .PHI.s changes in
accordance with the rotation angle of the fixing roller 41. This
represents that the inclination angle of the sheet S with respect
to the conveying path R1 changes in accordance with the rotation
angle of the fixing roller 41.
[0135] The image forming apparatuses according to the
above-described first and second embodiments calculate the movement
amount in accordance with the ratio between the index distance and
the reference distance. Accordingly, the movement amount (conveying
speed) of the sheet S calculated by the image forming apparatuses
according to the above embodiments changes in accordance with the
rotation angle of the fixing roller 41. Actually, however, the
conveying speed of the sheet S does not change in accordance with
the rotation angle of the fixing roller 41. Therefore, the image
forming apparatus according to the third embodiment calculates the
movement amount of the sheet S using an average value of the index
distances acquired while the fixing roller 41 makes at least one
rotation.
[0136] For example, a ratio between an average value of the index
distances .PHI.1-.PHI.200 and the reference distance .PHI.s in the
distribution 930 is approximately equal to the ratio indicated by
the distribution 920. Therefore, the image forming apparatus
according to the third embodiment can mainly correct an error in
the movement amount due to the inclination of the image capturer 70
using the average value of the index distances acquired during a
rotation cycle of the fixing roller 41.
[0137] (Control Structure of Calculator 90B)
[0138] FIG. 10 is a diagram for explaining a control structure of
the calculator 90B according to the third embodiment. Note that
members denoted by the same reference numerals as those in FIG. 4
are the same and therefore the description thereof will not be
repeated.
[0139] The calculator 90B differs from the calculator 90 described
with reference to FIG. 4 in that the calculator 90B includes a
distance correction unit 900 instead of the distance correction
unit 460.
[0140] The calculator 90B calculates temporary movement amounts 1,
2, . . . , 199 based on the Nth image and the (N+1)th image (N=1,
2, . . . , 199) by the actions of a discrete Fourier transform unit
410, a normalization processing unit 420, a synthesis unit 430 and
an inverse discrete Fourier transform unit 440. The variable N may
be the number of images continuously captured (generated) while the
fixing roller 41 makes one rotation. Note that, in another aspect,
the variable N may be the number of images continuously captured
while the fixing roller 41 makes at least one rotation. In yet
another aspect, the variable N may be the number of images
continuously captured over a period of an integral multiple of the
rotation cycle of the fixing roller 41.
[0141] In addition, an index distance calculation unit 450
calculates the index distances .PHI.1, .PHI.2, . . . , .PHI.200
from the Nth image (N=1, 2, . . . , 200) and outputs these index
distances to the distance correction unit 900.
[0142] The distance correction unit 900 calculates an average value
of the input index distances .PHI.1, .PHI.2, . . . , .PHI.200
(hereinafter also referred to as "average index distance"). The
distance correction unit 900 calculates the ratio of the reference
distance .PHI.s to the average index distance. The distance
correction unit 900 calculates an average value of the temporary
movement amounts 1, 2, . . . , 199 input from the inverse discrete
Fourier transform unit 440 (hereinafter also referred to as
"average temporary movement amount"). The distance correction unit
900 can calculate the movement amount of the sheet S by multiplying
the average temporary movement amount by the calculated ratio
mentioned above. Note that, in another aspect, the distance
correction unit 900 may calculate a value by multiplying the
immediate input (calculated) temporary movement amount 199 by the
above ratio as the movement amount of the sheet S.
[0143] Note that, in the above example, the calculator 90B
calculates the movement amount in consideration of the eccentricity
of the fixing roller 41 arranged on the downstream side of the
irradiation position Sp of a laser light source 81. In another
aspect, the calculator 90B may calculate the movement amount in
consideration of the eccentricity of a driving roller 22 arranged
on the upstream side of the irradiation position Sp of the laser
light source 81.
[0144] (Flow of Control for Calculating Conveying Speed--Part
3)
[0145] FIG. 11 is a flowchart for explaining control for
calculating the conveying speed of the sheet S being conveyed,
according to the third embodiment. Note that processing denoted by
the same reference numerals as those in FIG. 5 is the same
processing and therefore the description thereof will not be
repeated.
[0146] In step S1110, an FPGA 86 as the calculator 90B calculates
the temporary movement amount N based on the Nth image and the
(N+1)th image. Furthermore, the FPGA 86 saves the calculated
temporary movement amount N in a ROM 92.
[0147] In step S1120, the FPGA 86 determines whether the variable N
has reached a predetermined number. The predetermined number is
assumed as 199, for example.
[0148] When the FPGA 86 determines that the variable N has reached
the predetermined number (YES in step S1120), the FPGA 86 advances
the processing to step S1130. On the other hand, when the FPGA 86
determines that the variable N has not reached the predetermined
number (NO in step S1120), the FPGA 86 advances the processing to
step S570.
[0149] In step S1130, the FPGA 86 calculates the average temporary
movement amount which is an average value of the calculated
temporary movement amounts. More specifically, the FPGA 86
calculates an average value of the predetermined number of
temporary movement amounts.
[0150] In step S1140, the FPGA 86 calculates the average index
distance which is an average value of the calculated index
distances. More specifically, the FPGA 86 calculates an average
value of the predetermined number+1 of index distances.
Furthermore, the FPGA 86 calculates a ratio of the reference
distance .PHI.s to the average index distance. Furthermore, the
FPGA 86 multiplies the average temporary movement amount by this
ratio to calculate the movement amount of the sheet S at the
capturing interval of a two-dimensional sensor 84.
[0151] In step S1150, the FPGA 86 determines whether the print job
has ended. When the FPGA 86 determines that the print job has ended
(YES in step S1150), the FPGA 86 ends the series of items of
processing. When the FPGA 86 determines that the print job has not
ended yet (NO in step S1150), the FPGA 86 returns the processing to
step S525.
[0152] According to the above configuration, the image forming
apparatus according to the third embodiment can calculate the
movement amount (conveying speed) of the sheet S in consideration
of the eccentricity of the roller. Thus, the image forming
apparatus according to the third embodiment can more precisely
calculate the movement amount (conveying speed) of the sheet S than
the image forming apparatuses according to the first and second
embodiments.
Fourth Embodiment
[0153] The image forming apparatus according to the third
embodiment calculates the ratio of the reference distance .PHI.s to
the average index distance after printing is started. An image
forming apparatus according to a fourth embodiment calculates this
ratio before printing is started. Note that the image forming
apparatus according to the fourth embodiment may have the same
configuration as that of the image forming apparatus according to
the third embodiment.
[0154] (Flow of Control for Calculating Conveying Speed--Part
4)
[0155] FIG. 12 is a flowchart for explaining control for
calculating the conveying speed of the sheet S being conveyed,
according to the fourth embodiment. Note that processing denoted by
the same reference numerals as those in FIG. 5 is the same
processing and therefore the description thereof will not be
repeated.
[0156] In step S1210, an FPGA 86 starts conveying the sheet S. In
step S1220, the FPGA 86 determines whether the variable N has
reached a predetermined number (for example, 200).
[0157] When the FPGA 86 determines that the variable N has reached
the predetermined number (YES in step S1220), the FPGA 86 advances
the processing to step S1230. On the other hand, when the FPGA 86
determines that the variable N has not reached the predetermined
number (NO in step S1220), the FPGA 86 advances the processing to
step S1225.
[0158] In step S1225, the FPGA 86 increments the variable N and
then returns the processing to step S530.
[0159] In step S1230, the FPGA 86 calculates a correction
coefficient. In this embodiment, the correction coefficient is a
ratio of the reference distance .PHI.s to the average index
distance which is an average value of the predetermined number of
index distances.
[0160] In step S1240, the FPGA 86 starts a printing operation. In
step S1250, the FPGA 86 generates two images captured by an image
capturer 70 at different timings.
[0161] In step S1260, based on the above two images, the FPGA 86 as
the calculator 90B calculates the temporary movement amount of the
sheet S between the capturing timings of these images.
[0162] In step S1270, the FPGA 86 multiplies the calculated
temporary movement amount by the correction coefficient to
calculate the movement amount of the sheet S.
[0163] In step S560, the FPGA 86 calculates the conveying speed of
the sheet S from the capturing interval set in step S510 and the
movement amount of the sheet S. The FPGA 86 outputs the calculated
conveying speed to a controller 6.
[0164] In step S1280, the FPGA 86 determines whether the print job
has ended. When the FPGA 86 determines that the print job has ended
(YES in step S1280), the FPGA 86 ends the series of items of
processing. When the FPGA 86 determines that the print job has not
ended yet (NO in step S1280), the FPGA 86 returns the processing to
step S1250.
[0165] According to the above configuration, since the correction
coefficient is calculated before printing is started, the image
forming apparatus according to the fourth embodiment can more
precisely calculate the movement amount (conveying speed) of the
sheet S under printing than the image forming apparatus according
to the third embodiment.
Fifth Embodiment
[0166] An image forming apparatus according to a fifth embodiment
can physically sense the rotation angle of an eccentric roller with
a sensor and mainly correct an error in the movement amount due to
the inclination of an image capturer 70 using a correction
coefficient according to this rotation angle.
[0167] FIG. 13 is a diagram for explaining a configuration example
of the image forming apparatus 1300 according to the fifth
embodiment. Referring to FIG. 13, the image forming apparatus 1300
differs from the image forming apparatus 100 described with
reference to FIG. 3 in that the image forming apparatus 1300
includes a rotation angle sensing sensor 1310 and includes a
calculator 90C instead of the calculator 90. The rotation angle
sensing sensor 1310 detects the rotation angle of a fixing roller
41. The rotation angle sensing sensor 1310 can be realized by, for
example, a Hall sensor. The rotation angle sensing sensor 1310
outputs the detected rotation angle to an FPGA 86.
[0168] Furthermore, a relationship table 1320 is additionally saved
in a ROM 92 of the image forming apparatus 1300. The relationship
table 1320 holds the rotation angle and the correction coefficient
in association with each other. In this embodiment, the correction
coefficient may be, for example, a ratio of a temporary index
distance acquired at the corresponding rotation angle to an average
value of temporary index distances acquired while the fixing roller
41 makes one rotation. The temporary index distance is the length
in the conveying direction of a speckle pattern included in an
image captured at the corresponding rotation angle. The image
forming apparatus 1300 according to the fifth embodiment can
acquire (update) the relationship table 1320, for example, when the
power is turned on.
[0169] (Control Structure of Calculator 90C)
[0170] FIG. 14 is a diagram for explaining a control structure of
the calculator 90C according to the fifth embodiment. Note that
members denoted by the same reference numerals as those in FIG. 4
are the same and therefore the description thereof will not be
repeated.
[0171] The calculator 90C differs from the calculator 90 described
with reference to FIG. 4 in that the calculator 90C includes an
index distance calculation unit 1410 instead of the index distance
calculation unit 450.
[0172] The index distance calculation unit 1410 calculates the
temporary index distance based on the input first image.
Furthermore, the index distance calculation unit 1410 accesses the
relationship table 1320 to acquire a correction coefficient
corresponding to the rotation angle detected by the rotation angle
sensing sensor 1310 at the capturing timing of the first image. The
index distance calculation unit 1410 multiplies the calculated
temporary index distance by the correction coefficient to calculate
the index distance .PHI.1 corresponding to the first image.
Similarly, the index distance calculation unit 1410 calculates the
index distance .PHI.2 corresponding to the second image. The index
distance calculation unit 1410 outputs the calculated index
distances .PHI.1 and .PHI.2 to a distance correction unit 460.
[0173] (Flow of Control for Calculating Conveying Speed--Part
5)
[0174] FIG. 15 is a flowchart for explaining control for
calculating the conveying speed of the sheet S being conveyed,
according to the fifth embodiment. Note that processing denoted by
the same reference numerals as those in FIG. 5 is the same
processing and therefore the description thereof will not be
repeated.
[0175] In step S1510, the FPGA 86 detects a rotation angle .theta.N
at the timing when the Nth image was captured (generated) based on
the output of the rotation angle sensing sensor 1310.
[0176] In step S1520, the FPGA 86 accesses the relationship table
1320 to acquire a correction coefficient corresponding to the angle
.theta.N. Furthermore, the FPGA 86 calculates the temporary index
distance based on the Nth image and multiplies this temporary index
distance by the correction coefficient to calculate the index
distance .PHI.N corresponding to the Nth image.
[0177] In step S1530, the FPGA 86 detects a rotation angle
.theta.N+1 at the timing when the (N+1)th image was captured
(generated) based on the output of the rotation angle sensing
sensor 1310.
[0178] In step S1540, the FPGA 86 accesses the relationship table
1320 to acquire a correction coefficient corresponding to the angle
.theta.N+1. Furthermore, the FPGA 86 calculates the temporary index
distance based on the (N+1)th image and multiplies this temporary
index distance by the correction coefficient to calculate the index
distance .PHI.N+1 corresponding to the (N+1)th image.
[0179] According to the above configuration, the image forming
apparatus 1300 according to the fifth embodiment can calculate the
movement amount (conveying speed) of the sheet S in consideration
of the eccentricity of the roller. Thus, the image forming
apparatus according to the fifth embodiment can more precisely
calculate the movement amount (conveying speed) of the sheet S than
the image forming apparatuses according to the first and second
embodiments.
[0180] [Other Configurations]
[0181] FIG. 16 is a diagram illustrating how a distanced between
the sheet S and the lens 83 varies. As described with reference to
FIG. 8, the sheet S is affected by the eccentricity of the rollers.
Accordingly, as illustrated in FIG. 16, the distance d between the
lens 83 serving as an imaging lens and the sheet S can vary.
Therefore, in order to avoid changing of the size of the speckle
pattern formed on the two-dimensional sensor 84 even if the
distance d varies, the lens 83 is preferably a lens having
telecentricity.
[0182] The above-described various items of processing are assumed
to be realized by one FPGA 86 but not limited thereto. These
various functions may be implemented in at least one semiconductor
integrated circuit such as a processor, at least one application
specific integrated circuit (ASIC), at least one digital signal
processor (DSP), at least one FPGA, and/or a circuit including
circuits having other arithmetic functions.
[0183] These circuits can realize the various functions indicated
above by reading one or more commands from at least one tangible
readable medium.
[0184] Such a medium takes the form of a magnetic medium (for
example, a hard disk), an optical medium (for example, a compact
disc (CD) and a DVD), a volatile memory, a memory of any type of
nonvolatile memory, and the like, but is not limited to this
form.
[0185] The volatile memory may include a dynamic random access
memory (DRAM) and a static random access memory (SRAM). The
nonvolatile memory may include a ROM and an NVRAM. A semiconductor
memory may be part of a semiconductor circuit together with at
least one processor.
[0186] Although embodiments of the present invention have been
described and illustrated in detail, the disclosed embodiments are
made for purposes of illustration and example only and not
limitation. The scope of the present invention should be
interpreted by terms of the appended claims. The scope of the
present invention is intended that all modifications within the
meaning and scope of the claims and the equivalents thereof are
included.
* * * * *